System and method for order fulfillment

ABSTRACT

A system includes a first mobile drive unit and a second mobile drive unit. The system also includes a first inventory holder, a second inventory holder, and a third inventory holder. An inventory station includes a first location and a second location and the inventory station operable to receive a first inventory item from the first inventory holder at the first location. The first inventory holder is transported by the first mobile drive unit. The inventory station is also operable to receive a second inventory item from the second inventory holder at the first location. The second inventory holder is transported by the second mobile drive unit. The inventory station is also operable to receive a third inventory item from the third inventory holder at the second location. The third inventory holder is fixed at the second location while the inventory station receives the first inventory item and the second inventory item.

RELATED APPLICATIONS

This application is a continuation of U.S. Ser. No. 13/343,458, filedJan. 4, 2012, and entitled “System and Method for Order Fulfillment.”

TECHNICAL FIELD OF THE INVENTION

The present disclosure relates generally to inventory managementsystems, and more specifically to a system and method for orderfulfillment.

BACKGROUND OF THE INVENTION

Modern inventory systems face increasing demands to efficiently fulfillorders despite increasing complexity and diversity of inventories andorders. Inventory systems suffering from inefficient use of systemresources face lower system throughput, unfinished or delayed tasks, andunacceptable response times. Accordingly, such inventory systems facethe challenge of making more efficient use of time, space, equipment,and manpower in order to meet those rising demands.

SUMMARY OF THE INVENTION

In accordance with the teachings of the present disclosure,disadvantages and problems associated with fulfilling orders ininventory management systems have been substantially reduced oreliminated. In particular, an inventory system is provided that includesan inventory station operable to receive inventory items from variousinventory holders.

In accordance with one embodiment of the present disclosure, a systemincludes a first mobile drive unit and a second mobile drive unit. Thesystem also includes a first inventory holder, a second inventoryholder, and a third inventory holder. An inventory station includes afirst location and a second location and the inventory station operableto receive a first inventory item from the first inventory holder at thefirst location. The first inventory holder is transported by the firstmobile drive unit. The inventory station is also operable to receive asecond inventory item from the second inventory holder at the firstlocation. The second inventory holder is transported by the secondmobile drive unit. The inventory station is also operable to receive athird inventory item from the third inventory holder at the secondlocation. The third inventory holder is fixed at the second locationwhile the inventory station receives the first inventory item and thesecond inventory item.

In accordance with another embodiment of the present disclosure a methodincludes receiving an order for a first inventory item, a secondinventory item, and a third inventory item. The first inventory item isreceived from a first inventory holder at a first location associatedwith an inventory station, and the first inventory holder is transportedto the inventory station by a first mobile drive unit. The secondinventory item is received from a second inventory holder at the firstlocation associated with the inventory station, and the second inventoryholder is transported to the inventory station by a second mobile driveunit. The third inventory item is received from a third inventory holderat a second location associated with the inventory station, and thethird inventory holder is fixed at the second location while the orderfor the first inventory item, the second inventory item, and the thirdinventory item is assembled.

Technical advantages of certain embodiments include the ability toprovide an inventory system with an inventory station operable toreceive inventory items from various inventory holders. Anothertechnical advantage may include the ability to keep an inventory holderat an inventory station containing certain inventory items while otherinventory holders carry other inventory items to the inventory station.The inventory items in the stationary inventory holder may be determinedbased on a product velocity, which may be higher than other inventoryitems. Thus, inventory items with a relatively high product velocity maybe available at the inventory station to fill orders while otherinventory items are received at the station by inventory holderstransported by mobile drive units. Another technical advantage may bethe ability to use the relative product velocities of inventory items,which may allow the inventory items that remain stationary at theinventory station to be changed based on changes in product velocity.One other technical advantage may include the ability to fill an orderfrom a combination of dynamically arriving inventory items arriving oninventory holders via mobile drive units and stationary inventory. Thestatic stationary inventory may be located in an inventory holdercapable of being transported by mobile drive units and/or may be locatedin a fixed array of inventory holders. Moving inventory from a mobileinventory holder to a fixed array of inventory holders may allow themobile inventory holder to be repurposed for other tasks. Inventorystations may use a combination of stationary inventory holders, fixedarrays of inventory holders, and dynamic inventory holders. In addition,particular embodiments may use any number of stationary inventoryholders and arrays and/or may use inventory holders of varyingdimensions and load carrying abilities. Moreover, stationary inventoryholders at inventory stations may be replaced with other stationaryinventory holders that can be dynamically replaced as appropriate.Likewise, inventory items may be dynamically removed from the fixedarray of inventory holders and/or replaced with other inventory items asappropriate. Accordingly, the efficiency of the inventory system mayincrease.

Other technical advantages of the present disclosure will be readilyapparent to one of ordinary skill in the art from the following figures,description, and claims. Moreover, while specific advantages have beenexplained above, various embodiments may include some, all, or none ofthose advantages.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and itsfeatures and advantages, reference is now made to the followingdescription, taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 is a diagram illustrating example embodiments of an inventorysystem;

FIGS. 2A to 2D are diagrams illustrating example embodiments ofoperation of an inventory system;

FIG. 3 is a flowchart illustrating an example embodiment of method forfulfilling an order in an inventory system; and

FIG. 4 is a flowchart illustrating another example embodiment of methodfor fulfilling an order in an inventory system.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention and its advantages are bestunderstood by referring to FIGS. 1 through 4, wherein like numeralsrefer to like and corresponding parts of the various drawings.

FIG. 1 is a diagram illustrating example embodiments of an inventorysystem 10 for fulfilling orders 40. Inventory system 10 includesmanagement module 15, mobile drive units 20, inventory holders 30,inventory holders 32, order holders 34, and inventory stations 50. Insome embodiments, inventory stations 50 may include an array 52 ofinventory holders. Inventory holders 30 interface with inventory station50 and may be arranged in a queue 60. In general, system 10 is capableof transporting inventory holders 30, inventory holders 32, and/or orderholders 34 between locations in workspace 70 to facilitate the efficientfulfillment of orders 40. Inventory holder 32 may be located atinventory station 50 such that inventory items from inventory holder 32are available while inventory items are received from inventory holders30 in queue 60. In some embodiments, inventory items from array 52 areavailable while inventory items are received from inventory holders 30in queue 60. In some embodiments, inventory items from inventory holders32 and array 52 are available while inventory items are received frominventory holders 30 in queue 60. Inventory holders 32 may be assignedand/or transported to inventory station 50 and/or inventory items may beassigned to array 52 based on minimizing the cost of transportinginventory items within inventory holders 30 to inventory station 50,where cost may be based on the number of tasks, travel distance, and/ortime required by mobile drive units 20 and/or other components ofinventory system 10. For example, inventory holders 32 may be assignedand/or transported to inventory station 50 as determined by productvelocity. Additionally or alternatively, inventory items may be assignedto array 52 as determined by product velocity.

Some inventory systems face large fluctuations in product velocity. Forexample, the release of a new product may spark a surge in orders forthose items. Product velocity may refer to the frequency of ordersrequiring particular inventory items and/or types of inventory itemswithin system 10 in a given time period. In some embodiments, productvelocity may refer to the relative numbers of each inventory item and/ortype of inventory item required and/or predicted to be required byorders within system 10. For example, an inventory item may have arelatively high product velocity if that inventory item is morefrequently required by orders 40 within system 10 as compared to otherinventory items. In some embodiments, product velocity may refer to thequantity demanded of a given inventory item in a given time period.Alternatively or in addition, product velocity may simply refer to thequantity of an inventory item requested by open and/or received orders40 within inventory system 10. Product velocity may be determined basedon past order information, present order information, known and/orexpected demand, and/or predicted future order information.

Management module 15 represents any suitable combination of hardware,software and controlling logic operable to coordinate the operation ofvarious components within system 10. In some embodiments, managementmodule 15 may include one or more processors, one or more memorymodules, and one or more communication interfaces. Logic may be encodedon one or more non-transitory computer-readable media and may beexecuted by the one or more processors. Management module 15 may includelogic to schedule and execute various tasks involving the movement andprocessing of inventory items within system 10. For example, managementmodule 15 may assign tasks to mobile drive units 20 and/or inventorystations 50. Management module 15 may include logic to facilitatecoordination of the movement of mobile drive units 20 within workspace70 in order to complete the assigned tasks. Management module 15 mayinclude one or more communication interfaces to send information to andreceive information from mobile drive units 20. For example, managementmodule 15 may transmit, to one or more mobile drive units 20, taskassignment information, destination information, path planninginformation, reservation information, and/or any other appropriateinformation. Management module 15 may communicate information with oneor more inventory stations 50. Management module 15 may, in someembodiments, include logic to designate and/or assign inventory holders32 to inventory station 50. For example, management module 15 maydetermine the product velocity of inventory items in inventory system10. Management module 15 may additionally or alternatively include logicto assign inventory items to array 52. It should be noted that whilemanagement module 15 is depicted as a separate component withininventory system 10, the functionality performed by management module 15may be distributed over several devices. For example, the operations ofmanagement module 15 may be performed by mobile drive units 20 and/orother appropriate components of inventory management system 10. As aresult, any or all of the interaction between a particular mobile driveunit 20 and management module 15 that is described below may, inparticular embodiments, represent peer-to-peer communication betweenmobile drive units 20.

Management module 15 may determine one or more inventory itemsresponsive to orders 40 for one or more inventory items. Managementmodule 15 may determine which inventory holders 30 store those inventoryitems. In some embodiments, management module 15 may, alternatively oradditionally, determine whether those inventory items are stored ininventory holder 32 and/or array 52. Management module 15 may thenassign tasks to transport those inventory holders 30 to queue 60 atinventory station 50. Inventory holders 30 may transport inventory itemsneeded for order 40 that are not in inventory holder 32 and/or array 52.Based on their respective task assignments, mobile drive units 20 maytransport the inventory holders 30 with inventory items responsive toorder 40 to inventory station 50.

Management module 15 may replenish inventory items at inventory stations50 in any suitable manner. For example, management module 15 maydetermine, in some embodiments, that a quantity of inventory items ininventory holder 32 and/or array 52 has fallen below a threshold and/ormay determine that some other rule for replenishing inventory itemsstationed at inventory station 50 has been triggered. In response,management module 15 may assign another inventory holder 32 that holdsan additional quantity of inventory items to replace inventory holder 32and/or may assign a task to remove inventory holder 32 from inventorystation 50. Management module 15 may additionally or alternativelyassign inventory holder 32 to another inventory station 50 operable toreplenish inventory items into inventory holder 32. In some embodiments,management module 15 may assign a task to transport inventory holder 30containing an additional quantity of the given inventory item to queue60 so that those inventory items may be received into inventory holder32 and/or array 52. Accordingly, management module 15 may provide forthe replenishment of the inventory items in inventory holder 32 and/orarray 52 at inventory station 50.

It should be noted, however, that while various mobile drive units 20are depicted as arriving at inventory station 50 in a queue 60, thatneed not necessarily be the case. For example, in some embodiments,inventory station 50 may include more than one location at whichinventory station 50 may receive inventory items from inventory holders30. In such embodiments, mobile drive units 20 may transport inventoryholders 30 to those locations in parallel. After the inventory station50 receives needed inventory items from a given inventory holder 30, forexample, one mobile drive unit 20 may move that inventory holder 30 awayfrom inventory station 50. Then, another mobile drive unit 20 maytransport a different inventory holder 30 to the location recentlyexited by the previous inventory holder 30.

Management module 15 may assign a task to inventory station 50 tocomplete all or part of order 40 for one or more inventory items. Forexample, management module 15 may assign a task to a user or toinventory station 50 identifying inventory items to be selected for anorder 40. Management module 15 may also identify bins of inventoryholders 30, inventory holder 32, and/or array 52 that are storing theinventory items needed for order 40. Thus, management module 15 maytransmit various instructions to inventory station 50 to guide a user atinventory station 50 through the packing of a given order 40. Afterreceiving an indication that all or part of order 40 is complete,management module 15 may assign a task to transport order 40 in orderholder 34 to be stored for future delivery and/or shipped to adestination. In the case where order 40 is only partially completed,management module 15 may assign a task to transport order 40 to anotherinventory station 50 to receive additional inventory items.

Mobile drive units 20 represent any suitable combination of devices andcomponents operable to move inventory holders 30, inventory holders 32,and/or order holders 34 within workspace 70. Mobile drive units 20 maybe designed to couple, interface, dock or otherwise connect withinventory holders 30, inventory holders 32, and/or order holders 34. Forexample, mobile drive units 20 may be configured to move beneath a giveninventory holder 30, inventory holder 32, and/or order holder 34 andlift the holder using a docking head or other appropriate couplingstructure. Mobile drive units 20 may be capable of moving to anyappropriate location within workspace 70. Mobile drive units 20 mayinclude appropriate communication devices to communicate information toand from management module 15, other mobile drive units 20, and/orinventory stations 50. In some embodiments, mobile drive units 20 maycommunicate with management module 15 and/or other mobile drive unitsusing Wi-Fi (IEEE 802.11), Bluetooth (IEEE 802.15), Infrared DataAssociation standards, or any other appropriate wireless communicationsprotocol. Mobile drive units 20 may include appropriate sensors todetect fixed locations and/or other mobile drive units 20 withinworkspace 70. Mobile drive units 20 may thereby facilitate movementand/or avoid collisions. Mobile drive units 20 may communicateinformation to management module 15 to assist management module 15 inthe management of inventory system 10. For example, mobile drive unit 20may transmit its location relative to a fixed location within workspace70 to management module 15. In some embodiments, mobile drive units 20represent independent self-powered devices. Alternatively or inaddition, mobile drive units 20 may represent multiple types of mobiledrive units. Mobile drive units 20 in various embodiments may refer toany appropriate means of transporting inventory items to locationswithin inventory system 10. For example, mobile drive units may refer toconveyance systems that make use of conveyor belts, cranes, or otherapparatus to move inventory items and/or inventory holders 30 withininventory system 10.

Inventory holders 30 store inventory items. In some embodiments,inventory holders 30 include multiple storage bins each capable ofholding one or more inventory items. Alternatively or in addition,inventory holders 30 may include a rack of shelves, each shelf capableof carrying one or more inventory items. Inventory holders 30 arecapable of coupling and/or docking with mobile drive units 20 and beingcarried, rolled or otherwise moved by mobile drive units 20. Inventoryholder 30 may include a plurality of faces. Each bin of inventory holder30 may be accessible through one or more faces of the inventory holder30. For example, in some embodiments, inventory holder 30 may includefour faces, mobile drive unit 20 may be operable to rotate inventoryholder 30 at appropriate times within workspace 70 to present aparticular face containing the inventory items needed at an inventorystation 50.

Inventory holders 32 also store inventory items. Inventory holders 32are assigned to a location at inventory station 50 to remain stationarywhile orders are filled. Accordingly, inventory items in inventoryholders 32 are available for order 40 while inventory items are receivedfrom inventory holders 30 in queue 60. In some embodiments, inventoryholders 32 are substantially similar to inventory holders 30. Forexample, in some embodiments, inventory holders 30 may merely bedesignated as inventory holders 32 by management module 15. In someembodiments, a given inventory holder 32 may be assigned to inventorystation 50 based on the product velocity of one or more inventory itemsstored in the inventory holder 32. Accordingly, inventory items ininventory holders 32 at inventory station 50 may be used to fillmultiple orders 40. Inventory holders 32 may carry a number of inventoryitems that are the same and/or that may have a characteristic in common.For example, a characteristic in common may be that each inventory itemhas been assigned a discounted price in a given time period. Anothercharacteristic in common may be that each inventory item is associatedwith a certain time of year, such as a holiday period. One othercharacteristic in common may be that each inventory item is frequentlypurchased by a subset of customers in orders 40.

Order holders 34 store orders 40. For example, order holders 34 mayrepresent various pallets, bins, receptacles, tables, conveyors, and/orother structures capable of holding and/or storing orders 40. In someembodiments, order holders 34 may be an inventory holder 30 or 32 thatis designated to store orders 40. Order holders 34 may store orders 40until those orders are ready to be shipped. In some embodiments, orderholders 34 may themselves be loaded for shipment. For example, orderholders 34 may be shipping containers, pallets, or other receptaclessuitable for shipment. Order holders 34 may simply hold orders 40 untilthose orders are ready to be removed from order holders 34 for shipment.Alternatively or in addition, order holders 34 may store orders receivedby inventory system 10 that may be filled from inventory holders 30,array 52, and/or inventory holders 32 at inventory station 50. In someembodiments, order holders 34 are substantially similar to inventoryholders 30. For example, in some embodiments, inventory holders 30 maybe designated as order holders 34 by management module 15. Moreover, aparticular component may at different times serve as an inventory holder30, inventory holder 32, and/or order holder 34. In some embodiments, acomponent may serve simultaneously as both an inventory holder 30 and anorder holder 34 by storing both inventory items and orders 40. In someembodiments, order holders 34 may be capable of storing, holding and/orenclosing shipping containers such as boxes, pallets, or other shippingcontainers in which orders can be delivered to a given destination. Insome embodiments, order holders 34 may not include bins or partitionsand may instead hold only a single order 40 or group of orders 40 thatare stored in mass. For example, order holder 34 may support, include orrepresent a pallet in which one or more orders are stored. Moreover, inparticular embodiments, order holder 34 may represent a shippingcontainer on or in which stored orders 40 may be shipped.

Orders 40 each represent a collection of one or more inventory items. Insome embodiments, management module 15 may receive an order representinga customer request for various inventory items. In some embodiments,management module 15 may manage multiple orders 40 within inventorysystem 10. Orders 40 may be assembled at inventory stations 50 usinginventory items transported to inventory station 50 by mobile driveunits 20. For example, order 40 may be assembled from inventory itemsstored in various inventory holders 30, array 52, and/or inventoryholders 32. Orders 40, as used herein, may represent all or part of anactual customer order. For example, a customer order may include variousparts or portions, each including multiple inventory items. Order 40 mayrefer to one or more of those parts or portions.

Inventory stations 50 represent locations within workspace 70 designatedfor the completion of particular tasks involving inventory items. Suchtasks may include the removal of inventory items from inventory holders30 and/or inventory holders 32, the introduction of inventory items intoinventory holders 30 and/or inventory holders 32, and/or the counting ofinventory items in inventory holders 30 and/or inventory holders 32. Insome embodiments, tasks include the introduction to, removal from,and/or counting of inventory items in array 52. In some embodiments,tasks may include the decomposition of inventory items for pallet orcase-sized groups and/or may include assembling orders 40 for shipmenton or storage on order holders 34. Alternatively or in addition, tasksperformed at inventory station 50 may involve processing or handlinginventory items and other suitable functions. For example, individualorders 40 may be built and/or packed for shipment. As another example,manufactured products may be built and/or assembled from individualparts. In some embodiments, inventory stations 50 may simply representphysical locations within workspace 70 where a particular task involvinginventory items may be completed. In alternative embodiments, inventorystations 50 may represent the physical location and equipment forprocessing or handling inventory items. Such equipment may include, forexample, scanners for monitoring the flow of inventory items in and outof inventory system 10. Inventory stations 50 may include communicationinterfaces for communicating with management module 15. In someembodiments, inventory stations 50 may include displays and/or otherhuman machine interfaces. For example, inventory stations 50 may includedisplays for communicating tasks and other information to and from aworker or inventory manager at inventory station 50. Inventory stations50 may be controlled by human operators or may be fully automated. Humanor automated operators at inventory stations 50 may be capable ofperforming certain tasks involving inventory items such as packing orcounting inventory items. As depicted, certain inventory stations 50 maybe capable of interfacing with inventory holders 30 arranged in a queue60 and/or interfacing with inventory holders 32 at inventory station 50.In addition or in the alternative, inventory station 50 may include anarray 52 of inventory holders, which may store various inventory items.Inventory stations 50 may receive inventory items from inventory holders32 and/or array 52 while inventory items are received from successiveinventory holders 30.

Array 52 represents any suitable combination of bins, shelves, holdersor other structures suitable to store multiple inventory items atinventory station 50. In some embodiments, array 52 may include one ormore individually identifiable locations for storing inventory items.Accordingly, management module 15 may assign particular inventory itemsinto particular locations of array 52. Management module 15 may assigninventory items to those locations based on product velocity and/orother factors, as discussed in more detail below. In addition, whileinventory station 50 is illustrated as having a single array 52,inventory station 50 may have any number and combination of arrays 52.

Workspace 70 represents an area associated with inventory system 10 inwhich mobile drive units 20 may move and where inventory holders 30,inventory holders 32, and/or order holders 34 may be stored. Althoughthe illustrated figure shows an embodiment of inventory system 10 inwhich the overall workspace 70 is a particular geometric pattern,various embodiments of inventory system 10 may include a workspace 70that has variable dimensions or an arbitrary geometry. Accordingly,workspace 70 may be arranged in accordance with any appropriate geometrysuitable for a given inventory system 10. For example, workspace 70 mayhave multiple levels in accordance with the particular geometries of amulti-level warehouse. As another example, workspace 70 may be arrangedtaking into account particular features of an irregularly-shapedwarehouse and/or shipping zone. As yet another example, workspace 70 maybe arranged in accordance with a shipping dock and/or the deck of acargo ship.

As a result, while particular embodiments of inventory system 10 areillustrated, it should be appreciated that the teaching of the presentdisclosure may be applied to any type and number of inventory systems.For example, inventory system 10 may represent a mail order ore-commerce warehouse wherein individual orders 40 may be compiled atinventory stations 50 for shipment to individual customers. Inparticular embodiments, orders 40 may begin at an order inductioninventory station 50. At that inventory station 50, order inductionactivities may take place. For instance, boxes or other receptaclesoperable to hold each order 40 may be assembled. Other materials mayadditionally or alternatively be placed into the boxes or otherreceptacles, such as packing materials and/or information related toorders 40 (such as packing slips and/or bills of lading). In someembodiments, inventory holders 32 and/or arrays 52 may be located at theorder induction inventory station 50 such that inventory items may beused to at least partially fill orders 40 at order induction. The boxesand/or receptacles that hold or will hold inventory items associatedwith orders 40 may be loaded at that inventory station into orderholders 34 and transported to another inventory station 50. At thatinventory station 50, inventory items from inventory holders 30 and/or32 may be added to each partially completed order 40 to complete each ofthe orders 40. In some embodiments, however, a partially completed order40 may be transported to various inventory stations 50 to receiveinventory items at those inventory stations before the order 40 iscomplete. Once completed, orders 40 may be returned to order holders 34and/or may placed in another area suitable for shipment, such as on ashipping pallet or on a table or shelf. In some embodiments, shippingpreparation activities may take place at particular inventory stations50. At such inventory stations 50, various inventory items frominventory holders 30 and/or 32 may be added to the boxes and/orreceptacles that hold order 40 prior to shipment.

As another example, inventory system 10 may represent a merchandisereturn facility. In such embodiments, inventory items may representmerchandise returned by customers. Such merchandise may be stored ininventory holders 30, inventory holders 32, and/or array 52 whenreceived at the facility from individual customers. At appropriatetimes, large numbers of units may be removed from a particular inventoryholder 30, inventory holder 32, and/or array 52 and transferred atinventory station 50 to an order holder 34. Inventory items with a highreturn rate may be stored in inventory holders 32 and/or 52. Forexample, certain inventory items may be associated with a productrecall, causing those inventory items to be returned in high volume. Asanother example, inventory management system 10 may represent amanufacturing facility, and inventory items may represent individualcomponents of a manufacturing kit. Thus, individual items of themanufacturing kit may be stored in inventory holders 30, inventoryholders 32, and/or array 52. In some embodiments, partial assembliesand/or kits may be stored in array 52. Orders 40 for manufacturedproducts may be assembled from the individual items at inventorystations 50. Items of the manufacturing kit that will be and/or arelikely to be used multiple times during assembly may be stored ininventory holders 32 and/or array 52. Final products may be transportedby mobile drive units 20 using order holders 34 and may be shipped tothe appropriate destination. Thus, although a number of exampleembodiments are described in the present disclosure, inventory system 10may, in general, represent any suitable facility or system for storingor processing inventory items, and inventory items may represent objectsof any type suitable for storage, retrieval and/or processing in aparticular inventory system 10.

In operation, the various components of inventory system 10 completetasks associated with the fulfillment of orders 40 received and/orgenerated by inventory system 10. Management module 15 facilitates thescheduling and/or coordination of tasks within system 10. For example,management module 15 may assign tasks to various mobile drive units 20to transport various inventory holders 30 and/or inventory holder 32 toinventory station 50 in order to facilitate the fulfillment of orders.Management module 15 may, in some embodiments, assign tasks for mobiledrive units 20 to transport order holder 34 to various locations withinworkspace 70. Mobile drive units 20 may receive tasks from managementmodule 15. Mobile drive units 20, for example, may receive tasks totravel to various locations within inventory system 10. Mobile driveunits 20 may additionally or alternatively be assigned tasks to interactwith inventory holders 30, 32, and/or inventory stations 50. Forexample, mobile drive units 20 may be assigned one or more tasks totravel to a location of an inventory holder 30 or 32, transportinventory holder 30 or 32 to an inventory station 50, then undock frominventory holder 30 or 32, and/or move away from inventory station 50holding inventory holder 30 or 32.

Management module 15 determines the product velocity of variousinventory items within system 10. Management module 15 may determineproduct velocity based on analyzing orders 40 within inventory system 10and/or other information. Management module 15 may determine one or moreinventory items in inventory system 10 with relatively higher productvelocity than other inventory items in inventory system 10. Additionallyor alternatively, management module 15 may determine the frequencies oforders requiring inventory items within system 10. Management module 15may then determine one or more inventory items with relatively higherfrequencies of orders. In some embodiments, management module 15 mayadditionally or alternatively determine the average product velocity ofinventory holders 30 and/or 32 based on the product velocity ofinventory items stored in each inventory holder 30 and/or 32. Managementmodule 15 may accordingly determine relative average product velocitiesof inventory holders 30 and/or 32. Thus, management module 15 may selectinventory holders 30 and/or 32 with higher relative average productvelocities than other inventory holders 30 and/or 32.

Management module 15 may designate and/or assign inventory holders 32 toinventory station 50. Management module 15 may assign inventory holders32 based on minimizing the cost of transporting inventory items withininventory holders 30 to inventory station 50, where cost may be based onthe number of tasks, travel distance, and/or time required by mobiledrive units 20 and/or other components of inventory system 10. In someembodiments, the designation and/or assignment may be based ondetermining that inventory holder 32 is or is likely to hold inventoryitems required by a plurality of orders 40 within inventory system 10.For example, management module 15 may designate and/or assign inventoryholder 32 to inventory station 50 based on the product velocity of oneor more inventory items and/or the frequency of orders receiving one ormore inventory items within that inventory holder 32. In someembodiments, management module 15 may base the determination on thetotal number of each inventory items held by each inventory holder 30and/or 32 as well as the product velocity of those inventory items. Asan illustration, management module 15 may designate and/or assign aninventory holder 32 to inventory station 50 that holds ten of thesecond-highest velocity inventory items over an inventory holder 30 thatmerely holds one of the highest velocity inventory items. Accordingly,management module 15 may assign and/or designate inventory holder 32based on product velocity and number of inventory items within inventoryholders 30 and/or 32.

In some embodiments, the designation and/or assignment may be based oninventory items located at other inventory stations 50, based onattributes of inventory station 50, based on attributes of an operatorat inventory station 50, or based on other predictive measures. Forexample, one inventory station 50 may require a substantial number of acertain inventory item stored by an inventory holder 32 at thatinventory station 50 to complete orders 40. Meanwhile, a secondinventory station 50 may also require a number of those inventory itemsfor orders 40. Management module 15 may accordingly determine to moveinventory holder 32 to the second inventory station 50 so that a numberof those inventory items may be stored in array 52 at the secondinventory station 50. Management module 15 may determine to then moveinventory holder 32 back to the first inventory station 50. Accordingly,management module 15 may assign inventory holders 32 and/or inventoryitems to arrays 52 such that utilization of components of inventorysystem 10, such as mobile drive units 20, is minimized, or theperformance of the human operators is maximized.

In some embodiments, management module 15 may assign inventory holder 32to a fixed location at inventory station 50. Alternatively or inaddition, management module 15 may assign a task to transport inventoryholder 32 to inventory station 50. Based on a task assignment, a mobiledrive unit 20 may transport inventory holder 32 to inventory station 50.Inventory holders 32 may be assigned to inventory station 50independently of a given order 40. As the orders 40 within inventorysystem 10 change over time, management module 15 may be operable tocontinuously determine the product velocity of inventory items withinsystem 10. Thus, when another inventory item is determined to have ahigher product velocity than the inventory item in inventory holder 32,management module 15 may assign and/or designate another inventoryholder 32 to inventory station 50.

Management module 15 may also assign and/or designate inventory itemsfor array 52 based on determining that those inventory items are or arelikely to be required by a plurality of orders 40. Management module 15may assign inventory items to array 52 based on minimizing the cost oftransporting those inventory items to inventory station 50, where costmay be based on the number of tasks and/or time required by mobile driveunits 20 and/or other components of inventory system 10. In someembodiments, management module 15 may assign those inventory items toarray 52 based on the product velocity of one or more inventory itemsand/or the frequency of orders receiving one or more inventory items.Management module 15 may additionally or alternatively assign inventoryitems to array 52 based on inventory items that fit within array 52and/or on the number of inventory items that each bin and/or receptaclewithin array 52 is capable of holding. Management module 15 mayaccordingly sometimes select an inventory item with a relatively lowerproduct velocity based on determining that array 52 will hold a greaternumber of that item than a different inventory item that has arelatively higher product velocity. As an illustration, in an embodimentin which array 52 includes five storage bins, management module 15 mayassign five inventory items with the five highest product velocities tothe spaces in array 52. However, management module 15 may determine toselect the sixth highest product velocity item based on determining thatone or more of the highest five velocity inventory items will not fit ina receptacle of array 52. Alternatively, management module 15 maydetermine to select the sixth highest product velocity item based ondetermining that, for instance, array 52 is operable to receive ten ofthat item based on the item's size, but array 52 is only operable toreceive one of the highest product velocity item based on its size.

Management module 15 may assign tasks to various mobile drive units 20to transport the inventory holders 30 storing the assigned inventoryitems to inventory station 50. Accordingly, inventory station 50 mayreceive the assigned inventory items, and/or may cause those items to bemoved into array 52. When another inventory item is determined to have ahigher product velocity than one or more inventory items in array 52,management module 15 may assign a task to replace the inventory item inarray 52 with the inventory item having the higher product velocity.This may include, for example, assigning a task to transport aninventory holder 30 to inventory station 50 to store the inventory itemafter its removal from array 52. A task may also be assigned totransport inventory holder 30 storing the inventory item having thehigher product velocity to inventory station 50 for receipt into array52. In some embodiments, the inventory holder 30 having the higherproduct velocity may be used to store the inventory item after itsremoval from array 52. Thus, the inventory item in array 52 may bereplaced using a single inventory holder 30.

Inventory station 50 may receive a first inventory item from inventoryholder 30 for order 40 at a location at inventory station 50 and mayreceive a second inventory item for order 40 from another inventoryholder 30 at the same location once the first inventory holder 30 istransported away and the second inventory holder advances in queue 60 tothe first location. While orders are fulfilled, inventory holder 32 maybe located at another location at inventory station 50 and may provideinventory items while the inventory items from the first and secondinventory holders 30 are being received. In some embodiments, inventorystation 50 may receive inventory items into array 52 from inventoryholders 30 that are transported to inventory station 50 by mobile driveunits 20. In order to fulfill a given order 40, inventory station 50 mayreceive an inventory item responsive to order 40 from inventory holders30 transported to inventory station 50 by mobile drive units 20.Inventory station 50 may also receive inventory items from inventoryholder 32 and/or array 52 in order to fulfill order 40. Inventorystation 50 and/or a user of inventory station 50 may receive inventoryitems from the various inventory holders 30, inventory holder 32, and/orarray 52 and may assemble order 40 for delivery to an order holder 34.It should be noted, however, that while the illustrated embodimentdepicts order 40 as being delivered to order holder 34, order 40 may bedelivered to any appropriate destination, including a pallet, conveyor,and/or table. Thus, order 40 may be shipped to a given destinationand/or placed in storage for future delivery.

Management module 15 may assign various tasks to components of inventorysystem 10 to complete orders 40. In some embodiments, management module15 may assign tasks for various mobile drive units 20 to transportinventory holders 30 to inventory stations 50 so that inventory itemsstored within those inventory holders 30 may be used to complete orders40. In some embodiments, inventory system 10 may include variousinventory stations 50, with each inventory station 50 associated withone or more inventory holders 32 and/or array 52. Management module 15may thus determine an appropriate inventory station 50 at which tocomplete each order 40 based on the inventory items stored at eachinventory station 50. For example, management module 15 may choose aninventory station 50 that has one or more inventory items stationed ininventory holders 32 and/or array 52. By way of illustration, in anembodiment where inventory system 10 is a retail warehouse, oneinventory station 50 may be associated with inventory holders 32 and/orarrays 52 holding high velocity books while other inventory stations 50may be associated with inventory holders 32 and/or arrays 52 holdingother high velocity media. Based on determining that a given order 40includes high velocity books, management module may assign that order 40to the first inventory station 50 for completion. It should beunderstood that while a specific example of inventory items was used inthe preceding illustration, that the present disclosure applies to anynumber and types of inventory items. It should be understood, however,that utilizing the teachings of the present disclosure, managementmodule 15 may assign any number and combination of inventory holders 32to various inventory stations 50. In addition, management module 15 mayassign inventory items to any number and combination of arrays 52. Inparticular embodiments, inventory stations 50 may utilize both inventoryholders 32 and arrays 52 to complete orders 40. Additionally or in thealternative, various embodiments of inventory stations 50 may processorders using solely inventory holders 32 and/or arrays 52.

Moreover, while an example embodiment of operation has been explainedwith respect to illustrations in FIG. 1, it should be understood thatthe concepts of the present disclosure may be applied to any number andtypes of situations in which orders are fulfilled and/or processed. Morespecific examples of how orders may be fulfilled using the teachings ofthe present disclosure explained in more detail below with respect toFIGS. 2A-2D.

FIGS. 2A to 2D are diagrams illustrating example embodiments ofoperation of an inventory system 10.

As illustrated in FIG. 2A, an order 40 is fulfilled with inventory itemsfrom inventory holders 30 a, 30 b, 30 c, and 32. Inventory holders 30 a,30 b, and 30 c each carry inventory items to inventory station 50 via aqueue 60. Inventory holders 30 a, 30 b, and 30 c are transported toinventory station 50 by mobile drive units 20. Inventory holders 30 maybe carrying inventory items needed to complete an order 40. In someembodiments, mobile drive units 20 may carry each inventory holder 30 toinventory station 50 in response to a task assignment from managementmodule 15. As each inventory holder 30 reaches an interface location atinventory station 50, an inventory item needed by order 40 may bereceived by inventory station 50. While the items from inventory holders30 are received, inventory holder 32 remains stationary at a location atinventory station 50. Inventory holder 32 may be selected for thelocation at inventory station 50, for example, by management module 15based on the product velocity of inventory items held by the particularinventory holder 32. Accordingly, inventory holder 32 is selectedindependently of a given order 40. Thus, an order 40 may be fulfilled atinventory station 50 with items from inventory holders 30 a, 30 b, 30 c,and 32.

As illustrated in FIG. 2B, inventory holder 32 a may be replaced byinventory holder 32 b. For example, management module 15 may determinethat an inventory item held by inventory holder 32 b has a higherproduct velocity than inventory items held by inventory holder 32 a.Accordingly, management module 15 may assign inventory holder 32 b toremain stationary at inventory station 50 at the location previouslyheld by inventory holder 32 a. In some embodiments, inventory itemsremaining in inventory holder 32 a may be removed and/or returned toinventory holder 30 a, 30 b, and/or 30 c. Accordingly, those inventoryitems may be returned to storage or other appropriate destination. Insome embodiments, however, inventory holder 32 a may simply be returnedto a location within workspace 70 without removing inventory items fromits content. Additionally or alternatively, inventory holder 32 a may besupplemented by inventory holder 32 b and both may remain stationary atinventory station 50 at the same time at two locations at inventorystation 50. Thus, two or more inventory holders 32 may be designated toremain stationary at inventory station 50 and accordingly may beavailable to each provide inventory items for orders 40.

As illustrated in FIG. 2C, array 52 is first filled with inventory itemsand order 40 is then fulfilled using inventory items from inventoryholders 30 a, 30 b, 30 c, and array 52. Inventory items are firstreceived at inventory station 50 for introduction into array 52. As,illustrated, those inventory items are transported to the inventorystation by inventory holder 32. Alternatively or in addition, suchinventory items may be transported to inventory station by inventoryholders 30. Inventory items may be assigned to locations in array 52,for example, by management module 15 based on product velocity. Second,an order 40 is processed for fulfillment at inventory station 50. Itemsfrom inventory holders 30 a, 30 b, 30 c, and array 52 are received atinventory station 50 in order to fulfill order 40. In addition or in thealternative, inventory holder 32 may include additional inventory itemswith relatively high product velocities, such that inventory holders 32and array 52 may be utilized in the same embodiment. In addition,inventory station 50 may support any number and combination of inventoryholders 32 and arrays 52 as appropriate.

As illustrated in FIG. 2D, inventory items in array 52 are replaced byother inventory items. Management module 15 may, for example, determinethat one or more other inventory items have a higher product velocitythan one or more of those currently in array 52. Accordingly, theinventory items in array 52 may be moved to inventory holder 30 a and/or30 b, and inventory holder 30 c may carry replacement inventory items toinventory station 50. Alternatively, replacement inventory items frominventory holder 30 a and/or 30 b may be received into array 52 anditems being replaced may be moved to those same inventory holders. Whileinventory holders 30 are illustrated, it should be understood that itemsremoved from array 52 may be moved to inventory holders 32 and inventoryholders 32 may similarly transport the replacement inventory items.

While FIGS. 2A to 2D describe several specific scenarios forfacilitating the fulfillment of orders 40 using inventory holders 30,32, and/or arrays 52, the present disclosure is intended to encompassany number and combinations of inventory holders 30, 32, and/or arrays52 being utilized to fulfill various orders 40.

FIG. 3 is a flowchart illustrating an example embodiment of method 300for fulfilling an order in an inventory system 10. At step 302, aninventory station 50 is provisioned with first and second locations.First locations may be associated with queue 60 and may provide aninterface to receive items from inventory holders 30 transported toinventory station 50 by mobile drive units 20. The second location maybe designated for an inventory holder 32 to remain stationary whileorders 40 are being fulfilled.

At step 304, an inventory item for the second location is determined.For example, management module 15 may determine that a given inventoryitem in inventory system 10 has a higher product velocity than otherinventory items and/or may determine that an inventory item is requiredby a higher frequency of orders 40 than other inventory items.Accordingly, management module 15 may assign and/or designate aninventory holder 32 to remain at the second location while orders 40 arebeing fulfilled.

At step 306, management module 15 facilitates the transportation to thesecond location of the inventory holder 32 holding the inventory itemdetermined by management module 15. In some embodiments, inventoryholder 32 is transported to the second location by a mobile drive unit20. Inventory holder 32 will remain at the second location for so longas that inventory item remains designated by management module 15. If,however, management module 15 determines another inventory item to havea higher product velocity than the inventory item currently at inventorystation 50, management module 15 may assign a task to replace inventoryholder 32 holding the current inventory item with the new inventoryitem. Management module 15 may additionally or alternatively determinethat a quantity of inventory items in inventory holder 32 has fallenbelow a threshold. For instance, management module 15 may determine thatthe quantity of inventory items in inventory holder 32 is “low” or“empty.” In response, management module 15 may assign a task totransport an additional quantity of that inventory item to inventorystation 50 via a given inventory holder 30. In some embodiments,management module 15 may assign a task for a second inventory holder 32holding an additional quantity of that inventory item to replaceinventory holder 32 currently at inventory station 50.

At step 308, order 40 is received and/or generated by system 10 forvarious inventory items within system 10. Management module 15 may atstep 310 begin to process orders 40 within system 10. For example,management module 15 may process orders 40 by assigning various tasks tothe components of system 10 to complete order 40. Management module 15may determine that one or more inventory holders 30 carry variousinventory items required by order 40.

Accordingly, at step 312, management module 15 may determine whether anyinventory items on order 40 are already located at the second locationof inventory station 50. If the inventory item is already at the secondlocation at inventory station 50, then the inventory item is receivedfrom inventory holder 32 at the second location. At step 314, managementmodule 15 may then receive an indication that the inventory item isadded to order 40 from the second location. For example, inventorystation 50 and/or a worker at inventory station 50 may transmit a statusupdate or other indication that the inventory item is added to order 40.If the inventory item on order 40 is not located at the second location,then at step 316, management module 15 may determine which inventoryholder 30 within inventory system 10 holds the item. In someembodiments, multiple inventory holders 30 may hold the inventory itemrequired by order 40. Management module 15 may accordingly determine themost efficient route and/or closest inventory holder 30 containing thatinventory item.

At step 318, management module 15 facilitates the transportation to thefirst location of the inventory holder 30 that holds the requiredinventory item by mobile drive unit 20. For example, the first locationmay be an interface of inventory station 50 with the first inventoryholder 30 in queue 60. When inventory holder 30 reaches the firstlocation, the inventory item may be received from inventory holder 30into inventory station 50. At step 320, management module 15 may thenreceive an indication that the inventory item is added to order 40 fromthe first location. For example, inventory station 50 and/or a worker atinventory station 50 may transmit a status update or other indicationthat the inventory item is added to order 40. If at step 324, order 40is not complete, then method 300 continues processing order 40 at step312 until order 40 is complete. If order 40 is complete, the methodends. In some embodiments, however, the method may return to step 310 sothat another order 40 can be processed.

It should be noted, however, that method 300 is merely illustrated as anexample. Modifications, additions, or omissions may be made to method300 illustrated in the flowchart of FIG. 3. For example, managementmodule 15 is capable of assigning many tasks at once and/or in parallel.Thus, management module 15 may also process many orders in paralleland/or in sequence. Additionally, the steps of FIG. 3 may be performedin parallel or in any suitable order. Moreover, while FIG. 3 has beendescribed with respect to an embodiment having two locations, it isenvisioned that the teachings of the present disclosure may encompassinventory stations having any number and combinations of locations,including multiple locations for inventory holders 30 and/or multiplelocations for inventory holders 32.

FIG. 4 is flowchart illustrating another example embodiment of method400 for fulfilling an order 40 in inventory system 10. At step 402, aninventory station 50 is provisioned with an array 52 of inventoryholders. At step 404, an inventory item for array 52 may be determined.For example, management module 15 may determine an number of inventoryitems corresponding to the number of inventory holders in array 52 thathave the highest product velocity in inventory system 10. Managementmodule 15 may thus assign those inventory items to the inventory holdersin array 52 based on their relative product velocities.

At step 406, management module 15 facilitates the transportation toinventory station 50 of the inventory items assigned to array 52. Theinventory items, may for example, be transported to inventory station 50by mobile drive units 20. At step 407, those inventory items arereceived by inventory station 50 for introduction into array 52. Ifarray 52 is determined to be full at step 408, the management module 15may proceed to step 410. If array 52 is not full, then the methodreturns to step 404 to determine another inventory item to assign toarray 52. For example, management module 15 may determine an inventoryitem with the next highest product velocity. Management module 15 maythus continue to assign inventory items to array 52 until a number ofinventory items have been assigned corresponding to the number ofinventory holders in array 52. It should be noted, however, that whilestep 408 of the illustrated example embodiment of operation depicts adetermination of whether array 52 is full, array 52 need not be fullprior to processing order 40. In some embodiments, management module 15may determine, prior to filling array 52, that inventory system 10 doesnot have enough inventory items with the appropriate criteria to beintroduced into array 52. For example, various inventory items may haveapproximately the same product velocity and/or inventory items with highproduct velocity may be scarce and/or too large to fit into array 52.

After array 52 is determined to be full at step 408, orders may bereceived and/or generated within inventory system 10 at step 410. Order40 is processed at step 412. Management module 15 may, for example,assign tasks to the various components of inventory system 10 to processorder 40. At step 414, management module 15 may determine whether aninventory item on order 40 is in array 52. If it an inventory items isin array 52, then that inventory item may be received from array 52 intoinventory station 50. At step 416, management module 15 may then receivean indication that the inventory item is added to order 40 from array52. For example, inventory station 50 and/or a worker at inventorystation 50 may transmit a status update or other indication that theinventory item is added to order 40.

If the inventory item is not in array 52 at step 414, management module15 may then, at step 418, then determine which inventory holder 30within inventory system 10 holds the item. In some embodiments, multipleinventory holders 30 may hold the inventory item required by order 40.Management module 15 may accordingly determine the most efficient routeand/or closest inventory holder 30 containing that inventory item. Oncethe inventory holder 30 holding that inventory item is determined, thenmanagement module 15 may issue a task for a mobile drive unit 20 totransport that inventory holder 30 to inventory station 50.

At step 420, management module 15 facilitates the transportation toinventory station 50 of the inventory holder 30 that holds the requiredinventory item may be transported by mobile drive unit 20. Wheninventory holder 30 reaches inventory station 50, the inventory item maybe received from inventory holder 30 into inventory station 50. At step422, management module 15 may receive an indication that the inventoryitem is added to order 40. For example, inventory station 50 and/or aworker at inventory station 50 may transmit a status update or otherindication that the inventory item is added to order 40. If at step 424,order 40 is not complete, then method 400 continues processing order 40at step 412 until order 40 is complete. If order 40 is complete, method400 ends.

Technical advantages of certain embodiments include the ability toprovide an inventory system with an inventory station operable toreceive inventory items from various inventory holders. Anothertechnical advantage may include the ability to keep an inventory holderat an inventory station containing certain inventory items while otherinventory holders carry other inventory items to the inventory station.The inventory items in the stationary inventory holder may be determinedbased on a product velocity, which may be higher than other inventoryitems. Thus, inventory items with a relatively high product velocity maybe available at the inventory station to fill orders while otherinventory items are received at the station by inventory holderstransported by mobile drive units. Another technical advantage may bethe ability to use the relative product velocities of inventory items,which may allow the inventory items that remain stationary at theinventory station to be changed based on changes in product velocity.One other technical advantage may include the ability to fill an orderfrom a combination of dynamically arriving inventory items arriving oninventory holders via mobile drive units and stationary inventory. Thestatic stationary inventory may be located in an inventory holdercapable of being transported by mobile drive units and/or may be locatedin a fixed array of inventory holders. Moving inventory from a mobileinventory holder to a fixed array of inventory holders may allow themobile inventory holder to be repurposed for other tasks. Inventorystations may use a combination of stationary inventory holders, fixedarrays of inventory holders, and dynamic inventory holders. In addition,particular embodiments may use any number of stationary inventoryholders and arrays and/or may use inventory holders of varyingdimensions and load carrying abilities. Moreover, stationary inventoryholders at inventory stations may be replaced with other stationaryinventory holders that can be dynamically replaced as appropriate.Likewise, inventory items may be dynamically removed from the fixedarray of inventory holders and/or replaced with other inventory items asappropriate. Accordingly, the efficiency of the inventory system mayincrease. It should be noted, however, that method 400 is merelyillustrated as an example. Modifications, additions, or omissions may bemade to method 400 illustrated in the flowchart of FIG. 4. For example,management module 15 is capable of assigning many tasks at once and/orin parallel. Thus, management module 15 may also process many orders inparallel and/or in sequence. Additionally, the steps of FIG. 4 may beperformed in parallel or in any suitable order. Moreover, theembodiments described with respect to FIGS. 3 and 4 are expected befully combinable. It is therefore envisioned that various embodimentsmay include locations for various inventory holders 32 and arrays 52 atthe same time. Management module 15 may thus be capable of determiningthe optimal location for various inventory items within inventoryholders 30, 32, arrays 52, and/or various inventory stations 50.

Although the present invention has been described with severalembodiments, a myriad of changes, variations, alterations,transformations, and modifications may be suggested to one skilled inthe art, and it is intended that the present invention encompass suchchanges, variations, alterations, transformations, and modifications asfall within the scope of the appended claims. Moreover, while thepresent disclosure has been described with respect to variousembodiments, it is fully expected that the teachings of the presentdisclosure may be combined in a single embodiment as appropriate.

What is claimed is:
 1. An inventory system, comprising: a plurality ofinventory holders operable to store inventory items; and a workstationfor processing a plurality of orders and comprising a first defined arealocated at the perimeter of the workstation, wherein the first definedarea is designated for storing one or more inventory items associatedwith a product velocity and wherein the workstation is operable to:receive, at the first defined area and based at least in part upon adetermination of a first product velocity, a first inventory item from afirst inventory holder, wherein the first inventory item is associatedwith the first product velocity; receive a plurality of additionalinventory items from a plurality of additional inventory holders at asecond defined area located along a different portion of the perimeterof the workstation than the first defined area while the first inventoryholder remains at the first defined area; and receive, at the firstdefined area and based at least in part upon a determination of a secondproduct velocity, a second inventory item from a second inventoryholder, wherein the second inventory item is associated with the secondproduct velocity and wherein the second inventory holder is transportedto the first defined area from a location remote from the workstation.2. The inventory system of claim 1 further comprising a managementmodule, operable to: determine the first product velocity and the secondproduct velocity; initiate, based at least in part upon a determinationthat the first product velocity is or is predicted to be lower than thesecond product velocity, movement of the first inventory holder from thefirst defined area to a storage area; and initiate movement of thesecond inventory holder to the first defined area.
 3. The inventorysystem of claim 2, wherein the management module is further operable to:determine a first subset of the plurality of inventory holders thatcontain first inventory items that are ordered at a first rate that ishigher than a threshold rate of ordering, wherein the first inventoryholder is stationed at the first defined area in response to adetermination that the first inventory holder is in the first subset;determine a second subset of the plurality of inventory holders thatcontain second inventory items that are ordered at a second rate that islower than the threshold rate of ordering; determine, while the firstinventory holder is stationed at the first defined area, that the firstinventory item is subsequently ordered at the second rate that is belowthe threshold rate of ordering and, in response, assigning the firstinventory holder to the second subset; select the second inventoryholder from among the first subset of the plurality of inventory holdersto replace the first inventory holder at the first defined area; andinitiate movement of the second inventory holder to replace the firstinventory holder at the first defined area.
 4. The inventory system ofclaim 3, wherein the selection of the second inventory holder is basedat least in part upon a ranking of each inventory holder in the firstsubset of inventory holders.
 5. The system of claim 1, wherein the firstand second product velocities comprise past order information, knowndemand, and predicted future order information.
 6. The inventory systemof claim 1, wherein the first and second inventory holders aretransported to the first defined area by one or more mobile drive units.7. The inventory system of claim 2, wherein determining the firstproduct velocity comprises: monitoring a plurality of orders, whereinthe plurality of orders comprise requests for inventory items;determining a first number of first inventory items requested by theplurality of orders; determining, based at least in part upon the firstnumber of first inventory items, a frequency at which the firstinventory item is requested by the plurality of orders; and determiningthe first product velocity based at least in part upon the frequency. 8.The inventory system of claim 7, wherein determining the first productvelocity is further based at least in part upon predicting a secondnumber of first inventory items that are expected to be ordered on afuture plurality of orders.
 9. An inventory system, comprising: aplurality of inventory holders operable to store inventory items; afirst mobile drive unit configured to receive wireless instructions froma management module and independently transport one or more of theplurality of inventory holders within a workspace, the first mobiledrive unit operable to: transport, based at least in part upon adetermination of a first product velocity associated with a firstinventory item, a first inventory holder storing the first inventoryitem to a defined area associated with an inventory station configuredto process a plurality of orders, wherein the defined area is locatedalong a perimeter of the inventory station; a second mobile drive unitoperable to transport, based at least in part upon a determination of anoperation request to fulfill an order for the first inventory item and asecond inventory item, a second inventory holder storing the secondinventory item to a queue space associated with the inventory station,the inventory station configured to fulfill the order for the first andsecond inventory items, wherein the queue space is located along adifferent portion of the perimeter of the inventory station than thedefined area; and a third mobile drive unit operable to transport, basedat least in part upon a determination that the first product velocity isbelow a second product velocity associated with a third inventory item,a third inventory holder storing the third inventory item to the definedarea, wherein the third inventory holder replaces the first inventoryholder at the defined area.
 10. The inventory system of claim 9, whereinthe management module is further operable to: determine that a quantityof the first inventory item at the defined area is lower than athreshold; and assign a task to transport an additional quantity of thefirst inventory item to the defined area.
 11. The inventory system ofclaim 9, wherein the inventory station further comprises an array ofinventory holders operable to receive inventory items.
 12. The inventorysystem of claim 9, wherein transporting the first inventory holdercomprises: moving the first mobile drive unit to a location associatedwith the first inventory holder; docking the first mobile drive unitwith the first inventory holder at the location by moving underneath thefirst inventory holder and raising a docking head against a lowersurface of the first inventory holder; and moving the first mobile driveunit, while docked with the first inventory holder, to the inventorystation.
 13. The inventory system of claim 9, wherein the first mobiledrive unit is further operable to transport the first inventory holderfrom the defined area to a storage location remote from the inventorystation.
 14. The inventory system of claim 9, wherein the first andsecond product velocities are determined based at least in part uponpredicted future order information.
 15. A management module comprising:one or more interfaces operable to transmit wireless instructions to aplurality of mobile drive units; one or more processing units configuredto manage a flow of the plurality of mobile drive units and anassociated plurality of inventory holders towards spaces associated withan inventory station configured to process one or more orders, theinventory station associated with one or more queue spaces located alonga perimeter of the inventory station and one or more product velocityspaces located along a different portion of the perimeter of theinventory station than the queue spaces, the one or more productvelocity spaces designated for products having a product velocity abovea predetermined threshold, the one or more processing units operable to:facilitate fulfillment of a plurality of orders by transmitting wirelessinstructions to one or more of the plurality of mobile drive units totransport one or more inventory holders containing inventory itemsassociated with the plurality of orders to the inventory station; managetransportation of one or more first inventory holders containing one ormore first inventory items having a first product velocity above thepredetermined threshold to the one or more product velocity spaces; andmanage transportation of one or more second inventory holders containingone or more second inventory items having a second product velocity toreplace the one or more first inventory holders, in response to adetermination that the second product velocity is above thepredetermined threshold or the first product velocity is below thepredetermined threshold.
 16. The management module of claim 15, wherein:the first product velocity comprises an average of product velocities ofone or more first inventory items stored by the one or more firstinventory holders; and the second product velocity comprises an averageof product velocities of one or more second inventory items stored bythe one or more second inventory holders.
 17. The management module ofclaim 15, wherein: the one or more first inventory holders store one ormore of the first inventory item and one or more of the second inventoryitem; and the first product velocity comprises an average of the firstproduct velocity associated with the first inventory item and the secondproduct velocity associated with the second inventory item.
 18. Themanagement module of claim 15, wherein replacing the one or more firstinventory holders further comprises transporting, by one or more of theplurality of mobile drive units, the one or more first inventory holdersto a storage area remote from the inventory station.
 19. The managementmodule of claim 15, further operable to: monitor the plurality of ordersto determine an updated first product velocity; determine that theupdated first product velocity is below the predetermined threshold;monitor the plurality of orders to determine an updated second productvelocity; and determine that the updated second product velocity isabove the predetermined threshold.
 20. The management module of claim15, wherein the wireless instructions comprise at least a portion of apath to be traversed by one or more of the plurality of mobile driveunits.